Molecular insights into supercritical CO2 adsorption on calcium silicate hydrate

• Reveals atomic-scale mechanisms of supercritical CO₂ adsorption on C-S-H via molecular dynamics. • Demonstrates higher C/S ratios (≥ 1.5) greatly improve CO₂ adsorption and stabilit. • Shows 5 mol% hydration with low temperature optimizes CO₂ sequestration in cement. In carbon capture, utilization, and storage (CCUS) systems, cement is injected into the annular space between the well casing and the surrounding rock formation to create a zonal isolation barrier. This barrier prevents vertical migration of CO 2 along the wellbore, thereby ensuring long-term containment within the target reservoir and safeguarding well integrity. In subsurface CCUS environments, supercritical carbon dioxide (scCO 2 ) permeates calcium silicate hydrate (C-S-H), C-S-H the primary binding phase of cement. Molecular dynamics simulations investigate scCO 2 -C-S-H interactions at the molecular scale, by systematically varying calcium-to-silicon (C/S) ratios, hydration degrees, and temperatures. These variations elucidate the effects of interfacial chemistry on CO 2 adsorption and material responses. Lower demonstrates that elevated C/S ratios (≥1.5) increase CO 2 uptake through enhanced Ca–CO 2 coordination, while in aqueous scCO 2 containing 5 mol% water, hydroxyl-rich surfaces are stabilized and pore collapse is inhibited. Lower temperatures strengthen ionic bonding at the interface, enhancing CO 2 sequestration stability. These mechanistic insights reveal cement degradation pathways during scCO 2 -induced carbonation and provide foundational knowledge for designing durable wellbore cements, thereby ensuring long-term containment security in CCUS infrastructure.